Well stimulation apparatus and method

ABSTRACT

An intensifier unit includes a pair of sequentially operated reciprocating ram assemblies, novel valving systems for controlling the relative movement of the ram assemblies to effect an output of working fluid having a minimum of pressure fluctuations, and a novel pneumatic control system for controlling the valving systems in response to the positions of the ram assemblies. In the preferred embodiment, the unit is mounted on a truck for use in high pressure operations, such as well fracturing, erosion drilling, or the like, and the rams have relatively large diameters and relatively long strokes for providing a minimum of wear and fatigue cycles. In the method, the ram assemblies are returned quicker than they are extended, and are sequentially pressurized prior to initiation of their forward strokes and prior to the decompression of the stroke of the preceding working cylinder to provide an essentially uninterrupted pressure delivery of working fluid to the well.

United States Patent 1 Hall et al.

[ 1 Nov. 20, 1973 WELL STIMULATION APPARATUS AND METHOD [75] Inventors:Richard W. Hall, Springfield;

Richard H. Kerr, West Milton; Paul W. Padrutt, Springfield, all of Ohio1 [73] Assignee: Kelsey-Hayes Company, Springfield,

Ohio

[22] Filed:, Apr. 29, 1971 [21] Appl. No.: 138,568

[52] US. Cl. 417/345, 417/346 [51] Int. Cl. F04b 35/00 [58] Field ofSearch 417/399, 401, 900, 417/3, 4, 5, 6, 515, 342, 344-347 [56]References Cited UNITED STATES PATENTS 3,280,749 10/1966 Sennet et al.417/342 3,331,329 7/1967 Bauer 417/342 3,077,838 2/1963 Maglott 417/3463,234,882 2/1966 Douglas et al. 417/342 2,274,224 2/ 1942 Vickers417/250 3,205,906 9/1965 Wilkinson et a1. 417/900 X 3,327,641 6/1967Klosterman 417/900 X 3,477,380 11/1969 Johanson et al.. 417/3 3,507,3474/ 1970 Bennett 417/900 X Primary Examiner-William L Freeh AssistantExaminer-G. LaPointe Attorney-Marechal, Biebel, French & Bugg [57]ABSTRACT An intensifier unit includes a pair of sequentially operatedreciprocating ram assemblies, novel valving systems for controlling therelative movement of the ram assemblies to effect an output of workingfluid having a minimum of pressure fluctuations, and a novel pneumaticcontrol system for controlling the valving systems in response to thepositions of the ram assemblies. In the preferred embodiment, the unitis mounted on a truck for use in high pressure operations, such as wellfracturing, erosion drilling, or the like, and the rams have relativelylarge diameters and relatively long strokes for providing a minimum ofwear and fatigue cycles. In the method, the ram assemblies are returnedquicker than they are extended, and are sequentially pressurized priorto initiation of their forward strokes and prior to the decompression ofthe stroke of the preceding working cylinder to provide an essentiallyuninterrupted pressure delivery of working fluid to the well.

7 Claims, 5 Drawing Figures Nov. 20, 1973 United States Patent 1 Hall et31.

AVIA

L VI2A l I J mun-10mm 1915 3.7733138 mm 1 nr 4 IN VE N TORS HARD W.HALL, HAR KERR 8| PAUL W. DRUTT ATTORNEYS PATEN-IED NEW 20 I973 SHEET 3OF 4 PAlENIEnuuvzo I975 SHEET h []F 4 WELL STIMULATION APPARATUS ANDMETHOD BACKGROUND OF THE INVENTION Hydraulic well stimulation operationssuch as those involved in fracturing geological formations adjacent deepwell bores, erosion drilling, and the like present difficult problemsdueto the depth of the formation to be fractured, the high pressuresrequired to be generated, the corrosive and abrasive nature of thefluids to be pumped, the long pumping times, and various other factorsknown to persons skilled to the art.

In conventional practice, these operations are often performed by aseries of mechanically geared or revolving crank pumps having relativelyshort strokes and relatively high cycles per minute, for example 8 inchstrokes and 120 cycles per minute. Such pumps tend to fatigue and tobreak-down rather readily when used for well stimulation, because of theextreme pressures and the high cycles per minute rate of operation, andbecausethe working fluid is either abrasive (contains a high solids orsand concentration) or corrosive (contains a highhydrochloric acidconcentration) or both, which causes the valves and packings todeteriorate quickly.

Such pumpsalso exhibit pressure pulsations or transient fluctuationswhich aggravate the adverse effects created by the high rate of fatigueand wear cycles. As a result, effective and profitable well stimulationmay not have been realized.

The ideal hydraulic-well stimulating apparatus should have a pumpingsystem with the following features: First, it should have a long strokein order to reduce the number of fatigue and wear pressure cycles forlonger servicelife; Second, it should minimize the pressure fluctuationsin the output to minimize the strain on the pumping system; Third, itshould be capable of operating at pressures from l20,000psi or more tobe able to stimulate deep wells; Fourth, it should be portable, capableof being easily transported from site to site; Fifth, it should becapable of operating for long periods of time to stimulate hithertounstimulatable wells; and

Sixth, it should be inexpensive to operate and maintain.

SUMMARY OF THE INVENTION The present invention is directed to a newapparatus and method for pumping high pressure contaminated andcorrosive fluids at relatively high horsepower for "wen stimulationpurposes and the like. In general, the invention provides a two-cylinderintensifier which -maximizes volume per stroke and reduces the rate ofoperation using large diameter pumping rams having relatively longstrokes. 'The system circuit includes novel valve systems forcontrolling the supply of high pressure driving fluid to the rams and anovel control circuit for controlling the valve systems to effectmovement of the rams for converting high horsepower to a smooth, highpressure fluid flow with a minimum of fatigue cycles.

A high horsepower source, such as 1,100 horsepower turbine engine,drives a series of pumps, preferably of variable output, and these pumpsdeliver driving fluid at a high pressure to the power rams. The pressureof the driving fluid is in turn multiplied by the ram assemblies,wherein the diameters of the power rams are greater than the diametersof the pumping rams, and the working fluid is delivered to a well or thelike at an increased or multiplied pressure, for example l020,000 psi ormore, by alternating forward strokes of the ram assemblies. The strokesof the pumping rams are relatively long, for example inches, to minimizethe frequency of operation, and the consequent number of fatigue cyclesand total wear.

The ram assemblies are driven on their return strokes by a prechargedaccumulator which is adapted to return the ram assemblies quicker thanthey are extended in order that the returning ram may be pressurizedwhile the extending rarn decelerates. The ram assemblies, as controlledby the novel valve systems and the novel pneumatic control circuit,cooperate to produce a smooth, relatively pulseless output having arelatively constant pressure.

Each valve system comprises a control valve for admitting driving fluidto the ram to effect the forward stroke of the power ram, a pressurerelief valve for decompressing the power ram, at the completion of itsforward stroke, and an exhaust valve for exhausting the power ram afterits decompression to enable the return rams to effect the return stroke.Each system also includes a differential check valve for pressurizingthe power ram, prior to the admittance of driving fluid to the ram, to apressure less than the driving pressure to achieve a smooth transitionof output pressure as the rams reciprocate back and forth. In addition,each valve system includes a directional control valve for admittingdriving fluid to the differential check control valve before the ramstarts to extend and for admitting driving fluid to the exhaust valve tokeep this valve open while the ram returns.

The pneumatic control circuit, on the other hand, includes a relaycontrol valve and a holding valve for responding to the movement of eachram assembly, and a reversing valve actuated by the movement of both ramassemblies. The circuit is operatively connected to two pairs of tappetvalves, one for each ram assembly, which signal the completion of theforward and return strokes of the ram assemblies. The circuit respondsto actuation of the tappet valves and alternately pressurizes andactuates one ram while the other ram decelerates to reverse, bysequentially operating the valve systems, and provides a reliable meansof controlling the intensifier output and of achieving the objects ofthe invention.

One object of the present invention is to provide a reliable, efficientand dependable pressure multiplier with an optimized service life, andan improved method of fracturing wells and the like.

Another object is to provide a pressure multiplier with reducedfrequency of operation and with an increased stroke length and pumpingram diameter, so as to minimize wear and optimize valve life.

An important object isto provide a means for returning the rams fasterthan they are extended to provide a time interval, and to pressurize thereturn ram in that time interval to provide a smooth, relativelypulseless high pressure output.

These and other objects will become apparent from the drawings, thefollowing description and the appended claims.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing thetwo-cylinder fluid pressure intensifier of the present invention mountedon the bed of a truck;

,, FIG. 2 is an arrangement drawing of the partial system drawings shownin FIGS. 3A-C;

FIGS. 3A is a diagrammatic system drawing showing the intensifier ramassemblies, the air supply unit, the accumulator, the supply tank, andthe main valve station of the present invention;

FIG. 3B is a diagrammatic system drawing showing the pneumatic controlpanel of the present invention;

FIG. 3C is a diagrammatic system drawing showing a main pumping unit foruse in the practice of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodimentconsists of a two-cylinder fluid pressure multiplier or intensifierwhich converts high pressure driving fluid flow into a smooth multipliedhigh pressure working fluid output especially adapted for fracturinggeological formations adjacent well bores or the like. The apparatusaccomplishes this result with a pair of intensifying ram assemblieshaving relatively long forward and return strokes and large diametersfor reducing the frequency of operation, and includes means foreffecting relative movement of the ram assemblies in a manner whichminimizes pressure fluctuations in the working fluid output to providefor improved efficiency and service life.

Referring generally to FIG. 1, the intensifier of the present inventionmay be conveniently mounted on the bed of a truck, and includes a pairof ram assemblies comprising pumping rams PA and PB which receiveworking fluid through inlets 20 and discharge working fluid throughoutlets 21 at the end of the truck, and power rams RA and RB connectedto the pumping rams PA and PB respectively. The truck carries a drivingfluid (preferably hydraulic oil) supply tank T1, and a high horsepowersource such as a turbine engine TMl drives a pair of main pumps P1 andP2 which deliver driving fluid from tank T1 to a valve station M1 whichsequentially admits fluid to the power rams RA and RB to effect theforward pumping strokes of the ram assemblies.

The intensifier also includes a precharged accumulator AC1 for driving apair of twin return rams QA and QB (rams QB are not shown in FIG. 1) toeffect the return strokes of the ram assemblies. A diesel engine D1drives a pair of small pumps (not shown) which supply the accumulatorAC1 and main pumps P1 and P2 respectively, and also a compressor (notshown) and the compressor supplies air to a pneumatic control panel APlmounted on one side of the truck and adapted to control the valvestation M1 in response to movement of the ram assemblies.

The intensifying Ram Assemblies Referring more specifically to FIG. 3A,a preferred embodiment of the invention is shown wherein the power ramsRA and RB have 9 inch diameters and are adapted to reciprocate on 70inch strokes within hyare connected at the opposite ends of each bridge,and

preferably on opposite sides of each pumping ram to move the ramassemblies on their return strokes.

Accumulator The accumulator ACI is pre-charged with driving fluid toabout 1,000 psi and has a pair of branch lines 35 and 36 including checkvalves V12A and V128 connected to the return ram cylinders 34. A smallauxiliary pump P3 (approximately 6 GPM) driven by the diesel engine D1is adapted to charge the accumulator by delivering fluid from the supplytank T1 through filter F2 to an intersection 38 to the accumulatorcharge line 40 connected to the accumulator AC1 and to lines 35 and 36.This branch circuit includes a pressure relief valve V6 adapted to spillfluid over to tank T1 when the pressure in lines 35 and 36 exceeds 1,000psi. The accumulator AC1 supplies 1,000 psi fluid to the return rams QAand QB to effect the return strokes of the intensifying ram assemblies,and receives fluid from the return cylinders 34 on the forward strokesof the pumping rams PA and PB. Pump P3 discharges at 1,000 psi and itsdischarge pressure is controlled by relief valve V13.

Main Hydraulic Pump Unit BPl Referring to FIGS. 3A and 3C, the mainhydraulic pump unit BPl may include any of a number of pumping means,preferably of variable output, for supplying fluid to the intensifierram assemblies. For purposes of the present disclosure, the unit BPl isshown as including a pair of Kelsey-Hayes 500600 HP hydraulic fluidpumps P1 and P2 driven in tandem by a variable speed 1800 rpm Solarturbine engine TMl and having a 1,100 hp or more output. The pumps P1and P2 are charged through a line 42 and filters FlA and FIB by asupercharging pump P4 (approximately 600 GPM) which is driven by thediesel engine D1 and whose output is controlled at psi by the pressurerelief valve V9.

Each pump P1 and P2 includes three six-piston sections which dischargethrough corresponding outlets 43-45 and 46-48, and outlets 44 and 47 arepreferably connected to outlets 45 and 48, respectively, so that onesection discharges through line 50 and S1 and two sections dischargethrough lines 52 and 53. The outputs of the pump P1 and P2 may be variedby control units PMl and PM2, respectively, each of which includes anunloading valve 54 consisting of a main by-pass and pressure reliefvalve 55 and a normally open pilot control valve 56.

Under normal operation, the pumps P1 and P2 deliver fluid through lines50-53 to a main fluid output line 60 connected to the main hydraulicvalve station M1. The pump unit BPl is preferably provided with meansfor changing the outlet pressure when the turbine speed is changed, forexample by a change in altitude, and includes a remote selector (notshown) adapted to selectively energize solenoid valves AV 1- 8A-D, toload selected pump sections according to the power available at theturbine. The selector is also used to protect the pumps P1 and P2 frombeing overloaded. A pressure sensing valve PV9 senses the pressure inline 50, and when the'pressure reaches 5,100 psi, actuates valves AV18Aand AV18C which in turn cause their corresponding control valves 54 tounload one section of each pump to tank T1, causing valve 55 to act as arelief valve, and the pumps run at two thirds ca- ..pacity. In thepresent illustration, a maximum load condition with only two sections ofeach pump operating is set at 6,500 psi at the pump outlet, and isselected by actuating solenoid valve AV18E, so that fluid is returnedthrough relief valve PVS to tank T1. Normally, however, the maximum loadcondition is 5,200 psi, and this pressure level ismaintained by reliefvalve PV6 also connected to return line 62.

The flow through lines 50-53 is controlled by the air actuated checkvalve PV8 which receives hydraulic fluid through line 65 from theauxiliary pump P3 (FIG. 3A). When valve PV8 is open, fluid is deliveredthrough check valve PV7 and thence through lines 50 and 52 to closecheck valves 66 and 67, and through line:.60 to lines 51 and 53 to closecheck valves 68 and 69. In this blocking mode, the fluid delivered bypumps P1 and P2 is diverted through the control units PMl and PM2 to thesupply tank T1 via check valves 71-74 and return line 62, or throughpressure relief valves 55 and return line 75.

Main Hydraulic Valve Station M1 The main valve station Ml (FIG. 3A)includes two identical valve systems VA and VB for controlling the fluidsupply from line 60 to the power rams RA and RB respectively. The valvesystems include pneumatically actuated shut-off valves VIA and V1Bhaving ports 1-3. 'When valves VIA and VlB are open (connecting ports1-2), they admit fluid from line 60 to the inlet ports 24 of the powerram cylinders 22 and 23 and effect the forward strokes of rams RA andRB.

The station M1 also includes pneumatically actuated directional controlvalves V2A and V2B having ports I-7 and loops LA and LB between controlvalves V2A and V2B and the inlets 24 of cylinders 22 and 23. The loopsLA and LB include decompression check valves V3A and V3B connected inparallel with differential check valves V4A and V4B, respectively, thelatter valves V4A and V4B being set at 150 psi less than the drivingpressure in line60.

The directional control valves V2A and V2B are movable betweenpressurizing and exhausting positions and are biased normally to thepressurizing position (connecting ports 2-5), so that fluid from line 60is normally delivered to the loops LA and LB enabling power rams RA andRB to be pressurized to 150 psi less than the working pressure of line60. When in their exhaust position (connecting ports 2-4), fluid fromline 60 flows into and opens exhaust valves VSA or VSB connected to theoutlets 25 of cylinders 22 and 23, and

permits the rams RA and RB to be exhausted.

The valve systems VA and VB are adapted to effect the forward stroke ofone ram while, at the same time, effecting the return stroke of theother ram at a faster rate, in order that the returning ram may bepressurized prior to its forward stroke. This feature enables thereturning rarn to reverse and precharge to 5,050 psi (150 psi less thanthe working pressure 5,200 psi) as the first ,extending ram deceleratesto reverse. This keeps high pressure fluctuations in the output to aminimum and insures that the intensifiers will deliver stable pressureoutput.

Pneumatic Control Panel Referring to FIGS. 3A-3B, the pneumatic controlpanel API is supplied with pressurized air from the air supply unit ASl,which includes an air tank supplied with air by a compressor 81 drivenby the diesel engine D1. The panel APll receives air from the tank 80through line 82 and includes a solenoid operated remote start/stopswitch AV16 and a manually operated start/stop switch AV12.

A directional control switch AVM having ports 14 is spring biased to thenormal operating position (connecting ports 1-2) and has a resetposition (connecting port 1-3). A reset circuit for returning the powerrams RA and RB to their starting positions is connected to port 3 ofswitch AV14, and a manual directional control valve AVll is connected toport 2 of switch AV 14. The valve AVll has two positions, position 1 forautomatic movement of the rams, and position 2 for inching movement ofthe rams.

When pulled out to position 1, valve AVll delivers air to intersection85 and through shuttle-valve AV9 to intersection 86 where the air isdiverted in three directions. Line 87 diverts air to the main pump unitBPI, line 88 diverts air to a reversing control valve AV7 having ports1-6 and thence to shut off valve VlA or VlB in the main valve stationM1, and line 89 diverts air to the relay valve AV3A. Branch line 90diverts air from line 87 to the relay valve AV3B. Air is also deliveredvia intersection 85 and line 91 to tappet valves AVIA- B and AV2A-B(FIG. 3A) positioned for actuation by the cams 31 at the forward andreturn extensions of the ram assemblies. A branch line 92 connects thisair to ports 6 of directional control valves V2A and V2B, biasing themin their pressurizing position.

It will be noted that the reversing control valve AV7 has two positions:position 1 (opening ports I-2) for admitting air to valve VlA throughcheck valve AV8A and line 94, and position 2 (opening ports 1-3) foradmitting air to valve VlB through check valve AV8B and line 95. PanelAPI also includes holding valves AV4A and AV4B having ports 1-4 andmovable between normally open positions (connecting ports l-2), andblocking positions (connecting ports 2-3). These valves are moved totheir blocking positions when air passes through valve AV7, to valveAV4A by air in line 97, and to valve AV4B by air in line 98.

When pushed in to position 2, valve AVlI delivers air to acrank-operated three-position inch controlvalve AVlt) spring biased toposition 3 which completely stops the flow of air and movement of therams.

In position I, valve AVlll) connects with valve station Sequence ofOperations Reset Before the operating cycle is commenced, the system isreset. To do this the diesel engine D1 is started and auxiliary pump P3fully charges the accumulator AC1 to 1,000 psi. Engine D1 also startsthe compressor 81 so that air passes through line 82 to the controlpanel API. The solenoid start/ stop valve AV16 is then energized, andthe manual start/stop valve AV12 is placed in the stop position. Thesystem reset valve AV14 is then depressed, held, and valve AV12 ispulled to the start position to connect air from line 82 to intersection100. The air branches via line 101 to hydraulic valve PV8, opening thisvalve and admitting fluid into the pump unit BPl, where it is blocked bycheck valves 66-69 and flows through line 60 to valve unit M1 at theaccumulator pressure 1,000 psi.

Air also branches from intersection 100 through line 102 to intersection103 and through shuttle valves AV17A and B and lines 104 and 105 toports 7 of directional control valves V2A and V2B, causing these valvesto counteract the pressure on ports 6 thereof and to connect ports 2 toports 4 and ports 3 to ports 5. Air also passes from line 102 via branchlines 107 and 108 through shuttle valves AV13A and AV13B to ports 4 ofair valves AV3A and AV3B, setting them in position 1.

The opening of valve PV8 feeds fluid from auxiliary pump P3 throughsupply line 60 and through ports 2-4 of valves V2A and V2B to openexhaust valves V5A and VSB and connect the main intensifier rams RA andRB to exhaust. With these main rams to exhaust, the accumulator AC1supplies oil to the small return rams QA and QB effecting the returnstrokes of both intensifier units. On completion of the return strokes,tappet valves AV2A and AV2B are depressed, completing the system resetcycle. The system reset valve AV14 is then released.

Neutral The system is then placed in the neutral or stop position. Withthe system in the cycle reset position, as de- Ram RA Forward Ram RBPrepressurized With the pumps recycling to tank, the system is ready tostart an automatic cycle. With both main power rams RA and RB fullyreturned and resting on tappet valves AV2A and AV2B, with all pumpsrunning, and with air valve AV7 in position 1, shown, the inch/autovalve AVll is pulled to position 1 to connect air to intersection 85from which it is diverted to the tappet valves AVlA-B and AVZA-B vialine 91 and to intersection 86 via shuttle valve AV9.

Since the tappet valves AV2A-B are initially engaged, air passes throughthese valves and through lines 110 and 111 via shuttle valves AVSA andAVSB and shuttle valves AV13A and AV13B to port 4 of relay valves AV3Aand AVSB, moving these valves to posi- Via line 88 through reversingvalve AV7 to port 3 of I control valve VIA, opening this valve andcommencing the forward stroke of ram RA, and through branch 97 to port 4of ram RA, and through branch 97 to port 4 of valve AV4A to hold thisvalve in blocking position. 3. Via line 89 to port 1 of relay valve AV3Awhere it is blocked.

The main pumps P1 and P2, when loaded, deliver fluid thru valve VlA intothe main intensifier cylinder 22, starting the forward stroke of powerram RA and displacing oil from the small return rams QA into theaccumulator AC1, or, the accumulator is fully charged, displacing fluidthrough relief valve V6 to tank T1. At the same time, driving fluidpasses through ports 2-5 of valve V2B to valve V4B in loop LB. Valve V4Bcloses when the pressure on the outlet port, which is connected tointensifier ram RB, reaches 150 psi less than the pressure in line 60,causing the intensifier ram RB to be pressurized to within 150 psi ofthe moving intensifier ram RA.

Ram RB Forward Ram RA Stops On the completion of the forward stroke ofintensifier ram RA, the tappet valve AVlA is depressed, causing air tobe admitted via line 115 and shuttle valve AV6A to port 1 of holdingvalve AV4A. However, since valve AV4A is still being held in a blockingposition by air on port 4 thereof, it remains blocked. Air is alsoadmitted via branch line 116 to port 5 of reversing valve AV7, operatingthis valve (connecting ports l-3 and ports 2-4) and effecting a transferof the air being delivered through line 88 from line 94 to line 95.Accordingly, air passes through check valve AV8B and is admitted vialine 95 to port 3 of valve VlB, opening this valve and permittingdriving fluid to be admitted to ram RB to commence the start of itsforward stroke. Air is also admitted via line 98 to port 4 of holdingvalve AV4B, moving this valve to its blocking position.

At the same time, but at a slower rate set by valve AV8A, port 3 ofvalve VlA exhausts via line 94 through valves AV8A and AV7, resettingvalve VIA to the closed position. This stops the forward movement ofintensifier ram RA. In this condition, ram RB is receiving the full mainpump output through valve VlB.

Reversal-Ram RA Returns and Pressurizes Ram RB Stops As the pressureexhausts from port 3 of VIA, port 4 of valve AV4A also exhausts, at thesame rate and at the same time, resetting valve AV4A and opening port 1to port 2. This allows air from the tappet valve AVlA to be admittedthrough valve AV4A to port 5 of relay valve AV3A, shifting this valve toposition 2 and connecting port 1 to port 2. The air in line 89 istherefore directed through this valve and through shuttle valve AV 17Ato port 7 of the directional control valve V2A via line 104,counteracting the air pressure against port 6 from line 92 and openingports 2-4 and ports 3-5. This action admits driving fluid to exhaustvalve VSA.

Cylinder 22 decompresses at a rate set by valve V3A, and on completionof decompression, exhaust valve VSA opens and exhausts ram RA throughvalve VA. With intensifier ram RA fully opened to exhaust, the chargedaccumulator AC1 actuates the small return rams QA and ram RA starts itsreturn stroke, first releasing tappet valve AVlA and, on completion ofthe return stroke, operating tappet valve AV2A. The releasing of tappetvalve AVlA exhausts port 5 of relay valve AVSA, and the operating oftappet AV2A admits air to port 4 of AVSA, causing this valve to move toposition 1 and block the air flow through line 89. The releasing oftappet valve AVlA also exhausts port 5 of reversing valve AV7 throughline 116. However, since this valve is not spring biased, it momentarilyremains in the reversed position until actuated again.

Meanwhile, the intensifier ram RB is still making its forward stroke,displacing fluid from the return rams QB into the accumulator AC1. Theintensifier ram RA is pressurized through valve V2A and sits at thestart of its forward stroke. On completion of the forward stroke of ramRB, the tappet valve AVlB is actuated and air is admitted via line 118,shuttle valve AV6B, and line 120 to port 6 of reversing valve AV7,moving this valve to position 1 and connecting port 1 to port 2. Air isalso admitted to port 1 of the blocked valve AV4B.

Rarn RA Forward Ram RB Prepressurized Again As it reverses, valve AV7supplies air through line 94 to open valve VIA, and this admits fluidfrom the main pump supply to cylinder 22, thereby starting ram RA on itsforward stroke again. Simultaneously, valve AV7 cuts ofi air pressure tolines 95 and 98, and consequently these lines exhaust through valve AV8Band valve AV7. The exhausting of line 95, as was the case for theexhausting of line 94, described previously, causes valve VlB to closeand cut off the supply of driving fluid to ram RB. As a result ram RBstops. The exhausting of line 98 releases valve AV4B, opening port 1 toport 2 thereof and enabling air in line 118 to actuate relay valve AV3Bto position 2, connecting port 1 to port 2.

This action enables air from branch line 90 to be admitted through relayvalve AV3B and shuttle valve AVl7B to port 7 of directional controlvalve V2B, opening ports 2-4 and'enabling driving fluid to be admittedto exhaust valve VSB. Cylinder 23 is accordingly decompressed at a rateset by valve V3B in loop LB, and on completion of a decompression,exhaust valve V5A opens and, under the pressure exerted by theaccumulator AC1 on return rams QB, and ram RB exhausts through valve V2Band starts its return stroke.

The system thus starts another cycle. The forward stroke takes a longerperiod of time to complete than the return stroke, in order that thereturning ram may be pressurized while awaiting its next forward stroke.in addition, the system, by pressurizing the returned ram to within 150psi of the forward moving ram, provides a smooth, relatively pulselessoutput flow which minimizes the mechanical wear on the valving andextends the service life of the system.

Adjustment of Ram RA or Ram RB A manual system is provided to set thetappet valves, check clearances, etc. Ram RA is adjusted by moving theair valve AVll to the inch position, position 2, thereby connecting theair supply to valve AV 10, and

to port 6 of reversing valve AV7, setting this valve in position 1.

From intersection 125, air passes through shuttle valves AVIS and AV9 tointersection 86 where it is diverted in three directions. Line 87supplies air to the solenoid valves AV 18A-E which control the supplypumps P1 and P2. Line 89 connects air to port 1 of relay valve AVSA,where it is blocked, and line 88 connects air through valves AV7 andAV8A to port 3 of VIA, thereby opening this valve and admitting drivingfluid from line 60 to ram RA, starting its forward stroke.

At the same time, branch. line 90 delivers air through relay valve AV3Band shuttle valve AV17B to port 5 of the directional control valve V2B,causing driving fluid to be admitted to valve VSB and effecting ram RBsreturn stroke.

Since all motion stops when valve AV10 is moved to position 3, ramRA'may be adjusted forwardly by intermittently moving valve AV10 intoposition 1 and into position 3 to effect inching movement.

Ram RE is similarly adjusted by pushing air valve AV10 to position 2.This connects air to intersections and 131. From intersection 131, airpasses through shuttle valve AV6A and holding valve'AV4A to port 5 ofrelay AV3A, actuating this valve to position 2, and also through line116 to port 5 of reversing valve AV7, also actuating this valve toposition 2. Air is also connected through line 132 and via shuttlevalves AVSB and AV13B to port 4 of relay valve AV3B, actuating thisvalve to position 1.

From intersection 130 air is diverted through shuttle valves AVl5 andAV9 to intersection 86, where it is again diverted in three directions.Air in line 87 is again supplied to solenoid valves AV18A-E. This time,however, air in branch line 90 is blocked at port 1 of relay AV3B; valveAV7 connects air in line 88 to port 3 of valve VlB, actuating this valveand admitting driving fluid to ram RB; to start its forward stroke; andair in line 89 passes through relay valve AVSA and shuttle valve AV17Ato port 7 of directional control valve V2A, actuating this valve andadmitting driving fluid to exhaust valve V5A effecting the return of ramRA.

Thus, by a similar pneumatic network, ram RB may be adjusted byintermittently moving valve AV10 into position 2 and into position No. 3(stop position). Only when this valve is moved to position 1 or 2 arethe main pumps loaded. During inch conditions, the tappet valves AV lA-Band AV2A-B are inoperative.

Emergency Stops During movement of either intensifier unit, an emergencystop can be efiected by depressing valve AVl2 or de-energizing valveAV16. These valves interrupt the air supply and exhaust the system. Thisaction immediately unloads the main pumps and stops any movement of theintersifier rams RA and RB.

It is therefore apparent that a pressure intensifier constructed inaccordance with the present invention provides certain desirablefeatures and advantages. For example, an intensifier using the turbineand main pumps described above has the following theoretical outputs:

-- 16,800 psi X 108 gpm 1,060 hp 1,500 rpm at 5,200

2/3 Pumps 21,000 psi X 72 gpm 980 hp 1,500 rpm at 6,500 psi Theintensifier is thus capable of driving high pressure output which isuseful for well fracturing purposes and the like.

Moreover, the intensifier is able to deliver high pressure output with aminimum of pressure fluctuation and at a variety of pressures so thatthe output consists of a smooth, relatively pulseless flow whichminimizes the power shocks on the intensifier. The intensifier is wellsuited to a long stroke, large diameter intensifier ram assembly, whichreduces the frequency of operation so that there are fewer fatigue andwear cycles on the valves producing improved service life and reducingthe overall maintenance expense.

In addition, the valve systems together with the pneumatic controlcircuit of the present invention operate to return the rams faster thanthey. are extended to provide a time interval in which the return ram ispressurized while the extending ram is decelerating to reverse. As soonas the extending ram reverses, the valve system and pneumatic controlcircuit operate the pressurized ram to provide the relatively pulselessoutput flow described above. The valve systems and pneumatic controlcircuit are unique and enable the intensifier to operate nearlycontinuously and relatively free of maintenance expense.

The foregoing features enable hitherto low yielding wells to befractured more economically than in the past, and also enable wellswhich have come untapped to be stimulated. The apparatus of the presentinvention, therefore, from the practical standpoint, provides asignificant advance in the art.

While the methods and forms of apparatus herein described constitutepreferred embodiments of the invention, it is to be understood that theinvention is not limited to these precise methods and forms ofapparatus,

.and that changes may be made therein without departing from the scopeof the invention.

What is claimed is:

l. Hydraulic well fracturing equipment including a first intensifierhaving a hydraulic ram and a second intensifier having a hydraulic ram,each said intensifier having a common outlet for delivering fracturingfluid at high pressure to a well or the like, a source of hydraulicoperating fluid under high pressure for operating said rams, maincontrol valves operable to apply fluid from said source to each of saidrams, adjustable decompression valves operable to bleed off thehydraulic pressure from each of said rams, relatively larger valves foreach of said rams providing for rapid exhaust of the hydraulic fluidtherefrom, and pneumatic control means responsive to the approach of oneof said intensifier rams toward the end of its stroke for performing thefollowing steps in sequence 1. open the main control valve to the otherof said intensifiers to start its ram on a working stroke,

2. close the main control valve to said one intensifier ram,

3. operate the decompression valve of said one ram to bleed offhydraulic pressure therefrom, and

4. operate said larger exhaust valve of said one ram to provide for therapid exhaust of the fluid therefrom.

2. The fracturing equipment of claim 1 further comprising means forreturning said one intensifier to its starting position at a rate whichsubstantially exceeds the movement of said other intensifier under theinfluence of said hydraulic pressure, and valve means forprepressurizing said one intensifier to a pressure somewhat less thanthe working pressure of said other intensifier.

3. The system of claim 2 in which said prepressurizing means includes adifferential check valve.

4. In an intensifier having first and second reciprocating ramcylinders, a source of driving fluid at a driving pressure, means foreffecting the return strokes of said ram cylinders, pneumatic controlindicators positioned for actuation by said ram cylinders on theirforward and return strokes, a pair of identical first and second valvesystems for controlling the forward and return strokes of said ramcylinders, said first valve system comprising:

a directional control valve connected to said driving fluid source andmovable to a prepressurizing position in response to actuation of theindicator on the return stroke of a first ram cylinder and to anexhausting position in response to actuation of the indicator on theforward stroke of said first ram cylinder, differential check valveconnected between said first ram cylinder and said directional controlvalve for prepressurizing said first ram cylinder in response tomovement of said directional control valve to its prepressurizingposition, pressure release valve operatively connected between saidfirst ram cylinder and said directional control valve for decompressingsaid first ram cylinder in response to actuation of the indicator on theforward stroke of said first ram cylinder,

an exhaust valve operatively connected between said first ram cylinderand said directional control valve for exhausting said first ramcylinder in response to movement of said directional control valve toits exhausting position, and

a control valve connected to the driving fluid source and responsive toactuation of the indicator on the forward stroke of a second ramcylinder to admit driving fluid to said first ram cylinder to effect itsforward stroke.

5. In well fracturing equipment, the improvement comprising:

at least two sequentially operating reciprocating working cylinders forsupplying a working fluid under high pressure to the well,

a separate ram cylinder connected for operating each of said workingcylinders,

a source of driving fluid under pressure,

means for delivering the driving fluid to said ram cylinders at adriving pressure,

a separate valve system for each ram cylinder, including means forprepressurizing each ram cylinder to 13 14 a pressure less than saiddriving pressure, means for under high pressure to the well, admittingdriving fluid to each ram cylinder at said a separate ram cylinderconnected for operating each driving pressure to effect its forwardstroke, and of said working cylinders, means for decompressing andexhausting each ram 3 Source of i i fl id under pressure, y at thecompletlon of its forward Stroke, 5 means for delivering the drivingfluid to said ram cyla bridge member operatively connected betweeninders at a driving pressure 621?}! ram y f and each f Cylmder aaseparate valve system for each ram cylinder, includof F cylmdersoperatlveiy connected ing means for prepressurizing each ram cylinder toGael; g g effechtmg F a pressure less than said driving pressure, meansfor es 0 Sal ram Cy m ers at t 6 Comp anon o 10 admitting driving fluidto each ram cylinder at said their forward strokes, d

rlvmg pressure to effect its forward stroke, and and control means forcontrolling said valve systems means for decompressmg and exhaustingeach ram and said return cylinders to effect return strokes of said ramcylinders at a rate substantially faster than said forward strokesthereof to provide time for prepressurization of said ram cylinders forenabling said ram cylinders to produce a smooth, relatively continuousand pulseless output flow of said working fluid to said well. 6. Theequipment of claim 5 wherein said actuating means comprises apre-charged accumulator connected to said return cylinders.

cylinder at the completion of its forward stroke, return cylindersoperatively connected to effect the return strokes of said ram cylindersat the comple tion of their forward strokes, and control means forcontrolling said valve systems and said return cylinders to effectreturn strokes of said ram cylinders at a rate substantially faster thanprepressurization of said ram cylinders for enabling 7. In Wellfracturing equipment, the improvement said ram cylinders to produce asmooth, relatively comprising: continuous and pulseless output flow ofsaid workat least two sequentially operating reciprocating ing fluid tosaid well.

working cylinders for supplying a working fluid said forward strokesthereof to provide time for

1. Hydraulic well fracturing equipment including a first intensifierhaving a hydraulic ram and a second intensifier having a hydraulic ram,each said intensifier having a common outlet for delivering fracturingfluid at high pressure to a well or the like, a source of hydraulicoperating fluid under high pressure for operating said rams, maincontrol valves operable to apply fluid from said source to each of saidrams, adjustable decompression valves operable to bleed off thehydraulic pressure from each of said rams, relatively larger valves foreach of said rams providing for rapid exhaust of the hydraulic fluidtherefrom, and pneumatic control means responsive to the approach of oneof said intensifier rams toward the end of its stroke for performing thefollowing steps in sequence
 1. open the main control valve to the otherof said intensifiers to start its ram on a working stroke,
 2. close themain control valve to said one intensifier ram,
 3. operate thedecompression valve of said one ram to bleed off hydraulic pressuretherefrom, and
 4. operate said larger exhaust valve of said one ram toprovide for the rapid exhaust of the fluid therefrom.
 2. close the maincontrol valve to said one intensifier ram,
 2. The fracturing equipmentof claim 1 further comprising means for returning said one intensifierto its starting position at a rate which substantially exceeds themovement of said other intensifier under the influence of said hydraulicpressure, and valve means for prepressurizing said one intensifier to apressure somewhat less than the working pressure of said otherintensifier.
 3. The system of claim 2 in which said prepressurizingmeans includes a differential check valvE.
 3. operate the decompressionvalve of said one ram to bleed off hydraulic pressure therefrom, and 4.operate said larger exhaust valve of said one ram to provide for therapid exhaust of the fluid therefrom.
 4. In an intensifier having firstand second reciprocating ram cylinders, a source of driving fluid at adriving pressure, means for effecting the return strokes of said ramcylinders, pneumatic control indicators positioned for actuation by saidram cylinders on their forward and return strokes, a pair of identicalfirst and second valve systems for controlling the forward and returnstrokes of said ram cylinders, said first valve system comprising: adirectional control valve connected to said driving fluid source andmovable to a prepressurizing position in response to actuation of theindicator on the return stroke of a first ram cylinder and to anexhausting position in response to actuation of the indicator on theforward stroke of said first ram cylinder, a differential check valveconnected between said first ram cylinder and said directional controlvalve for prepressurizing said first ram cylinder in response tomovement of said directional control valve to its prepressurizingposition, a pressure release valve operatively connected between saidfirst ram cylinder and said directional control valve for decompressingsaid first ram cylinder in response to actuation of the indicator on theforward stroke of said first ram cylinder, an exhaust valve operativelyconnected between said first ram cylinder and said directional controlvalve for exhausting said first ram cylinder in response to movement ofsaid directional control valve to its exhausting position, and a controlvalve connected to the driving fluid source and responsive to actuationof the indicator on the forward stroke of a second ram cylinder to admitdriving fluid to said first ram cylinder to effect its forward stroke.5. In well fracturing equipment, the improvement comprising: at leasttwo sequentially operating reciprocating working cylinders for supplyinga working fluid under high pressure to the well, a separate ram cylinderconnected for operating each of said working cylinders, a source ofdriving fluid under pressure, means for delivering the driving fluid tosaid ram cylinders at a driving pressure, a separate valve system foreach ram cylinder, including means for prepressurizing each ram cylinderto a pressure less than said driving pressure, means for admittingdriving fluid to each ram cylinder at said driving pressure to effectits forward stroke, and means for decompressing and exhausting each ramcylinder at the completion of its forward stroke, a bridge memberoperatively connected between each ram cylinder and each workingcylinder, a pair of return cylinders operatively connected to eachbridge member for effecting the return strokes of said ram cylinders atthe completion of their forward strokes, and control means forcontrolling said valve systems and said return cylinders to effectreturn strokes of said ram cylinders at a rate substantially faster thansaid forward strokes thereof to provide time for prepressurization ofsaid ram cylinders for enabling said ram cylinders to produce a smooth,relatively continuous and pulseless output flow of said working fluid tosaid well.
 6. The equipment of claim 5 wherein said actuating meanscomprises a pre-charged accumulator connected to said return cylinders.7. In well fracturing equipment, the improvement comprising: at leasttwo sequentially operating reciprocating working cylinders for supplyinga working fluid under high pressure to the well, a separate ram cylinderconnected for operating each of said working cylinders, a source ofdriving fluid under pressure, means for delivering the driving fluid tosaid ram cylinders at a driving pressure, a separate valve system foreach ram cylinder, including means for prepressurizing each ram cylinderto a pressure less than said driving pressure, means for admittingdriving fluid to each ram cylinder at said driving pressure to effectits forward stroke, and means for decompressing and exhaUsting each ramcylinder at the completion of its forward stroke, return cylindersoperatively connected to effect the return strokes of said ram cylindersat the completion of their forward strokes, and control means forcontrolling said valve systems and said return cylinders to effectreturn strokes of said ram cylinders at a rate substantially faster thansaid forward strokes thereof to provide time for prepressurization ofsaid ram cylinders for enabling said ram cylinders to produce a smooth,relatively continuous and pulseless output flow of said working fluid tosaid well.